This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. An elevated plasma level of low density lipoprotein (LDL)-cholesterol is a major risk factor for atherosclerotic coronary artery disease (Gotto and Pownall, 1999). LDL comprises a neutral lipid core of cholesteryl esters (CEs) and triglycerides, surrounded by a surface monolayer of phospholipids, free cholesterol, and apolipopro-tein B-100 (apoB-100), which contains the ligand for the LDL-receptor (LDLR) that initiates LDL endocytosis, a key step in cholesterol metabolism. The molecular basis of LDL endocytosis would be better understood if we could determine the structure of the LDL/LDLR complex. We are interested in determining the cryo-EM structure of the LDL and LDLR complex.